1. Field of the Invention
The present invention relates to soft tissue implants, often referred to as prostheses. Such implants have particular utility for breast augmentation and breast reconstruction.
2. Related Background
Over the years, many attempts have been made to develop prostheses suitable for breast implants.
At first, breast augmentation was accomplished by means of injecting liquids, primarily silicone gel, directly into the soft tissue of the breast. That silicone gel, however, was soon found to migrate, causing serious medical problems. To solve the migration problem, the next step was to encapsulate the silicone gel in a pouch or envelope made of some impervious material, often silicone, and then surgically implant the pouch in the breast.
Unfortunately, that approach brought with it a new set of problems. It was soon found that the body's defense mechanisms cause the formation of a natural tissue capsule around the breast prosthesis thereby enclosing and isolating it from the surrounding body tissue. This fibrous tissue capsule, containing fibroblasts, myofibroblasts and inflammatory cells, has a continuous tendency to contract, thereby tightening around the implant and causing it to become very firm. Contracture can also lead to tenderness of the breast, pain, erosion of the adjacent tissue as well as other complications.
To further exacerbate the problem, studies have shown that the silicone gel fillers found in many breast prosthesis tend to "bleed" through the membrane envelope causing a chronic inflammatory response in the surrounding tissue. This chronic inflammatory response also leads to natural tissue encapsulation and eventually to contracture.
Numerous attempts have been made to overcome the contracture problem. For example, U.S. Pat. No. 4,298,998 proposes using a double walled or "dual lumen" prosthesis with an absorbable outer wall and an absorbable filler material between the inner and outer walls. U.S. Pat. No. 4,772,284 proposes using a more biocompatible filler material, for example, collagen gels and saline. U.S. Pat. No. 4,840,628 describes a prosthesis that has neither a liquid core nor a permanent enclosing membrane. Instead, it suggests using a cast silicone gel elastomer having a homogeneous cohesive structure throughout. In addition, that casting may be covered with a minimum membrane coating or an absorbable shell.
The present invention addresses the encapsulation/contracture/inflammatory response problems by using all natural materials rather than silicone or the like.